In that case, it is assumed that it is as follows.
i. SomeAction is implements SessionAware.
ii. And It is defined in struts-default.
iii. devMode is true or false.

["someValue"] of the name of "someKey" enters in SessionMap when the
request shown in that URL is processed.
It is meant that ["someValue"] is an array including "someValue".
This causes ClassCastException in case of almost.

hisato.killing@gmail.com
It is thought that this only has to be my mistake ,setting etc.